1. Field of the Invention
The present invention relates to a method for brazing a metallic honeycomb body, which is wound, laminated or intertwined from at least partly structured sheet-metal layers and which is to be brazed in at least some regions. The invention also relates to an apparatus for performing the method.
Metal honeycomb bodies are increasingly used as carrier bodies for catalytically active material in the exhaust systems of motor vehicles with internal combustion engines, for example. It is important for the durability of such catalyst carrier bodies as well as for the suitability of similar honeycomb bodies in another applications, that the individual sheet-metal layers which make up such bodies be joined together, at least in some regions, by high-quality brazed connections. Typically, such honeycomb bodies are of formed high-temperature-proof and corrosion-proof steel sheets and are vacuum-brazed at high temperature.
Such brazed honeycomb bodies are described, for instance, in German Published, Non-Prosecuted Applications DE 23 02 746 A, corresponding to British Patent No. 1,452,982; or German Published, Non-Prosecuted Applications DE 29 24 592 A, corresponding to U.S. Pat. No. 4,381,590. Those references already mention methods for applying brazing material, but such methods generally apply too much brazing material, so that on one hand the methods are not economical, and on the other hand the sheet properties are disadvantageously affected because the sheets tend to alloy with the brazing material.
Published European Application No. 0 049 489 B describes a method for applying glue and brazing material to such honeycomb bodies that already enables the application of only small quantities of brazing material. German Published, Non-Prosecuted Application DE 38 18 512 A, corresponding to U.S. application Ser. No. 621,068, filed Nov. 30, 1990, also describes methods for applying glue and brazing material to such carrier bodies and also includes an overview of the brazing application methods known at that time.
Methods used thus far have always included one problematic step at some point that led to difficulties in the production process or produced uneconomical results. In some methods, the sheets first had to be degreased by etching, which is labor-intensive and costly and requires disposal of the residues which are produced. The use of adhesives or pressure-sensitive adhesives also generally leads to the use of organic solubilizers, which once again necessitates additional provisions for environmental protection and is therefore uneconomical. Substances that evaporate in the vacuum furnace can also create difficulties in maintaining the vacuum.